Reus isn't stupid. If he ever leaves Bayern he'll only go to a team where he's guaranteed to start. He'll join anyone of Man City, Chelsea, Man Utd or Bayern if he ever decides to leave BVB.
He's not guaranteed to start in 3 out of 4 of these teams and if he's not stupid he'll see the flaws behind moving to such places.
1) City would buy him and offer a place over the inferior Navas or Jovetić, but the real question is where do Reus' ambitions lie? Because he certainly won't win a European Cup with them.
2) At Chelsea he'd probably have to gain enough trust from Mou before he started him without frequent rotations.
3) United are stupidly top heavy already and there is no guarantee of starting in their current system that needs to have Shrek in some shape or form on the field all the time. Why would that be a good move for either party I have no idea.
4) Nowhere near a guaranteed spot in Pep's team. Not that he'd even want to go there really. Last resort move and not a good one.
Truth is it's just not a good time for him to seek transfer. Barca and where he's at are probably the best fits for him. Maybe PSG too if he considered it.